--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -766,6 +766,19 @@ class revlog(object):
 
         raise RevlogError(_("No match found"))
 
+    def cmp(self, node, text):
+        """compare text with a given file revision"""
+        p1, p2 = self.parents(node)
+        return hash(text, p1, p2) != node
+
+    def makenode(self, node, text):
+        """calculate a file nodeid for text, descended or possibly
+        unchanged from node"""
+
+        if self.cmp(node, text):
+            return hash(text, node, nullid)
+        return node
+
     def diff(self, a, b):
         """return a delta between two revisions"""
         return mdiff.textdiff(a, b)